The drug discovery process is currently undergoing a fundamental revolution as it embraces `functional genomics`, that is, high throughput genome- or gene-based biology. This approach is rapidly superseding earlier approaches based on `positional cloning`. A phenotype, that is a biological function or genetic disease, would be identified and this would then be tracked back to the responsible gene, based on its genetic map position.
Functional genomics relies heavily on the various tools of bioinformatics to identify gene sequences of potential interest from the many molecular biology databases now available. There is a continuing need to identify and characterise further genes and their related polypeptides/proteins, as targets for drug discovery.
A number of polypeptide growth factors and hormones mediate their cellular effects through a signal transduction pathway. Transduction of signals from the cell surface receptors for these ligands to intracellular effectors frequently involves phosphorylation or dephosphorylation of specific protein substrates by regulatory protein serine/threonine kinases (PSTK) and phosphatases. Serine/threonine phosphorylation is a major mediator of signal transduction in multicellular organisms. Receptor-bound, membrane-bound and intracellular PSTKs regulate cell proliferation, cell differentiation and signalling processes in many cell types.
Aberrant protein serine/threonine kinase activity has been implicated or is suspected in a number of pathologies such as rheumatoid arthritis, psoriasis, septic shock, bone loss, many cancers and other proliferative diseases. Accordingly, serine/threonine kinases and the signal transduction pathways which they are part of are potential targets for drug design.
A subset of PSTKs are involved in regulation of cell cycling. These are the cyclin-dependent kinases or CDKs (Peter and Herskowitz, Cell 1994: 79, 181-184). CDKs are activated by binding to regulatory proteins called cyclins and control passage of the cell through specific cell cycle checkpoints. For example, CDK2 complexed with cyclin E allows cells to progress through the G1 to S phase transition. The complexes of CDKs and cyclins are subject to inhibition by low molecular weight proteins such as p16 (Serrano et al, Nature 1993: 366, 704), which binds to and inhibits CDK4. Deletions or mutations in p16 have been implicated in a variety of tumors (Kamb et al, Science 1994: 264, 436-440). Therefore, the proliferative state of cells and diseases associated with this state are dependent on the activity of CDKs and their associated regulatory molecules. In diseases such as cancer where inhibition of proliferation is desired, compounds that inhibit CDKs may be useful therapeutic agents. Conversely, activators of CDKs may be useful where enhancement of proliferation is needed, such as in the treatment of immunodeficiency.
Frequently, in diseases such as osteoporosis and osteoarthritis, patients have established lesions of bone or cartilage, respectively. Treatment of such lesions requires an agent that will stimulate new bone or cartilage formation to replace that lost to the disease; therefore, there is a need for drugs that increase the number of osteoblasts or chondrocytes, the cells responsible for bone or cartilage formation, respectively. Similarly, replacement of heart or skeletal muscle depleted by diseases such as myocardial infarction or HIV-associated cachexia requires drugs that stimulate proliferation of cardiac myocytes or skeletal myoblasts. The present invention describes a novel human clone, H2LAU20, which shares homology with predicted PSTK's from S. pombe, D. melanogaster, C. elegans, and S. cerevisiae and has motifs associated with other known protein kinases. Inhibitors of H2LAU20 are expected to regulate proliferation of cell growth.